Amnesty International says rebels carrying out a campaign of violence to silence their opponents.

Yemen's Houthi rebels have carried out a "chilling campaign to quash dissent", arresting and torturing their political rivals, according to a rights group.

The UK-based Amnesty International said on Wednesday that politicians, activists, journalists and academics were targeted and detained by the Houthis and their allies in 60 cases it looked at between December 2014 and March 2016.

The report said the incidents happened in the Houthi-held capital Sanaa, as well as the contested cities of Ibb, Taiz and Hodeidah. It said that many of those arrested had been held incommunicado for prolonged periods, suffering torture and other ill-treatment while being denied access to a lawyer or their family.

The Houthis - a rebel group backed by troops loyal to former president Ali Abdullah Saleh - have been fighting against forces that include southern separatists, tribal fighters and military loyal to current President Abd-Rabbu Mansour Hadi, who is in exile in Saudi Arabia.

"Houthi forces have presided over a brutal and deliberate campaign targeting their political opponents and other critics since December 2014," James Lynch, the deputy director of the Middle East and North Africa programme at Amnesty International, said.

"Hundreds of people have been rounded up and held without charge or trial, and in some cases they have been forcibly disappeared in flagrant violation of international law."

Some of the prisoners had been held for up to 17 months without being brought before a prosecutor or a judge, Amnesty said.

Many had been held in secret, makeshift detention centres, including private homes, and were transferred multiple times between different locations, it said.

One former detainee described to Amnesty how his interrogators tortured him for 90 minutes. He said he was blindfolded, had his hands tied and was beaten with a stick. His interrogators also gave him electric shocks to the chest, neck, forearms and groin, he alleged.

Earlier this month, Houthi officials told Amnesty that those in detention were being held "because they gave GPS coordinates to the Saudi Arabia-led coalition."

The Houthis, who hail from the northern highlands and champion the interests of the beleaguered Zaidi community which make up a fifth of Yemen's 25 million population, insist they are fighting to defend themselves against government aggression and marginalisation.

Saudi Arabia and other nations launched a military campaign against them in March 2015 after they advanced on on Yemen's second city, Aden, and forced Hadi to flee the country.

Since then, more than 6,400 people have been killed in the conflict and 2.8 million displaced, according to the United Nations.